Question 621276
How much of the job did press A get done in 1.5 hrs
from 8 AM to 9:30 AM?
A's rate is ( 1 job ) / ( 24 hrs )
In 1.5 hrs:
{{{ (1/24)*1.5 = .0625 }}} job/hr
Now both A and B work on job
There is {{{ 1 - .0625 = .9375 }}}
of the job left to do.
B's rate is ( 1 job ) / ( 12 hrs )
{{{ 1/24 + 1/12  = .9375 / t }}}
Multiply both sides by {{{ 24t }}}
{{{ t + 2t = 22.5 }}}
{{{ 3t = 22.5 }}}
{{{ t = 7.5 }}}
In 7.5 hrs after B starts, the job is done
9:30 + 7.5 = 5 PM job is done
check answer:
{{{ 1/24 + 1/12  = .9375 / t }}}
{{{ 1/24 + 1/12  = .9375 / 7.5 }}}
{{{ 1/24 + 2/24 = .125 }}}
{{{ 1/8 = .125 }}}
{{{ .125 = .125 }}}
OK